Fan Hub Stiffener

ABSTRACT

A fan hub stiffener is provided. The stiffener occupies a gap between parallel fan hub plates to reduce or eliminate stress on the plates during operation. The stiffener may include a body and arms extending radially outward from the body and into the spaces between adjacent fan blades.

TECHNICAL FIELD

The present disclosure relates generally to a fan hub, and, more particularly, to an apparatus for stiffening a fan hub by partially or completely filling the gap between the fan hub plates.

BACKGROUND

Fans are used in industry in a multitude of applications, including in radiators for cooling engines used in on road and off road vehicles. A fan may include blades and a hub used to hold the blades.

Fan blades may be made of metal or composite materials, and generally have the same size and shape (i.e., come from the same mold) in each fan. The number of blades per fan can be changed though hub machining changes. The diameter of the fan can also be changed by increasing the diameter of the fan hub.

The fan hub generally comprises two plates separated by a central hub connection, sometimes referred to as a spacer. The fan blades may be bolted to both plates of the hub. The plates are spaced apart to accommodate the roots of the blades, and so a gap may exist between the hub plates that runs from the central hub connection to the perimeter (outer diameter) of the hub.

The stiffness of such fan hubs may be lower than desired due to the spaced apart, two plate design. This low stiffness can result in a low frequency fore-aft bending mode that causes high stresses in multiple locations on the hub plates. The overall stiffness becomes even lower as the hub diameter is increased.

It is known to provide an annular plate located between two adjacent hub plates. For example, U.K. Patent Publication No. GB 2390647B describes an axial flow impeller having an annular plate located between two hub plates and having spring tags for improving the location of the blades with respect to the hub. While effective for its intended purpose, the annular plate is not designed to, and does not necessarily, stiffen the hub.

The present disclosure presents an apparatus for stiffening a fan hub and thus reducing hub stresses. While a number of exemplary configurations are described herein, it should be appreciated that the examples are not a limitation on the scope of this disclosure or of the attached claims except to the extent expressly noted.

SUMMARY

According to an aspect of the disclosure, a fan hub is provided comprising a front plate, a rear plate, an annular central hub connection and a stiffener. The front plate comprises an inner facing surface and an outer facing surface, and has a diameter and a perimeter. Likewise, the rear plate comprises an inner facing surface and an outer facing surface and has a diameter and a perimeter. The front plate and the rear plate each define a central bore, a plurality of sets of blade fastener apertures arranged circumferentially around the plate near the plate perimeter, a plurality of central hub connection fastener apertures arranged circumferentially around the central bore, and a plurality of stiffener fastener apertures. The central bore, the blade fastener apertures, the central hub connection fastener apertures and the stiffener fastener apertures of the rear plate register with the central bore, the blade fastener apertures, the central hub connection fastener apertures and the stiffener fastener apertures of the front plate. The central hub connection defines an inner bore which registers with the central bores of the front plate and the rear plate. The central hub connection has a cylindrical outer wall and further defines central hub connection apertures registering with the central hub connection fastener apertures of the front plate and the rear plate. The stiffener occupies a gap between the front plate and the rear plate and may comprise a body and a plurality of arms extending radially outward from a perimeter of the body. The body defines a stiffener central bore registering with central bores of the front plate and the rear plate. The stiffener has an outer diameter no larger than the diameter of the front plate. Each arm extends radially outward from the body and between adjacent sets of blade fastener apertures. The stiffener defines apertures for receiving fasteners. The stiffener apertures register with some or all of the stiffener fastener apertures in the front plate and the rear plate.

According to another aspect of the disclosure, a fan is provided comprising a fan hub and fan blades. The fan hub comprises a front plate, a rear plate, an annular central hub connection and a stiffener. The front plate comprises an inner facing surface and an outer facing surface, and has a diameter and a perimeter. Likewise, the rear plate comprises an inner facing surface and an outer facing surface and has a diameter and a perimeter. The front plate and the rear plate each define a central bore, a plurality of sets of blade fastener apertures arranged circumferentially around the plate near the plate perimeter, a plurality of central hub connection fastener apertures arranged circumferentially around the central bore, and a plurality of stiffener fastener apertures. The central bore, the blade fastener apertures, the central hub connection fastener apertures and the stiffener fastener apertures of the rear plate register with the central bore, the blade fastener apertures, the central hub connection fastener apertures and the stiffener fastener apertures of the front plate. The central hub connection defines an inner bore which registers with the central bores of the front plate and the rear plate. The central hub connection has a cylindrical outer wall and further defines central hub connection apertures registering with the central hub connection fastener apertures of the front plate and the rear plate. The stiffener comprises a body and a plurality of arms extending radially outward from a perimeter of the body. The body defines a stiffener central bore registering with central bores of the front plate and the rear plate. The stiffener has an outer diameter no larger than the diameter of the front plate. Each arm extends radially outward from the body and between adjacent sets of blade fastener apertures. The stiffener defines apertures for receiving fasteners. The stiffener apertures register with some or all of the stiffener fastener apertures in the front plate and the rear plate. The fan blades are affixed to the fan hub, with each blade comprising an inner portion located between the front plate and the rear plate.

In still another aspect of the disclosure, a machine is provided comprising a cooling system having a fan. The fan comprising a fan hub and fan blades. The fan hub comprises a front plate, a rear plate, an annular central hub connection and a stiffener. The front plate comprises an inner facing surface and an outer facing surface, and has a diameter and a perimeter. Likewise, the rear plate comprises an inner facing surface and an outer facing surface and has a diameter and a perimeter. The front plate and the rear plate each define a central bore, a plurality of sets of blade fastener apertures arranged circumferentially around the plate near the plate perimeter, a plurality of central hub connection fastener apertures arranged circumferentially around the central bore, and a plurality of stiffener fastener apertures. The central bore, the blade fastener apertures, the central hub connection fastener apertures and the stiffener fastener apertures of the rear plate register with the central bore, the blade fastener apertures, the central hub connection fastener apertures and the stiffener fastener apertures of the front plate. The central hub connection defines an inner bore which registers with the central bores of the front plate and the rear plate. The central hub connection has a cylindrical outer wall and further defines central hub connection apertures registering with the central hub connection fastener apertures of the front plate and the rear plate. The stiffener comprises a body and a plurality of arms extending radially outward from a perimeter of the body. The body defines a stiffener central bore registering with central bores of the front plate and the rear plate. The stiffener has an outer diameter no larger than the diameter of the front plate. Each arm extends radially outward from the body and between adjacent sets of blade fastener apertures. The stiffener defines apertures for receiving fasteners. The stiffener apertures register with some or all of the stiffener fastener apertures in the front plate and the rear plate. The fan blades are affixed to the fan hub, with each blade comprising an inner portion located between the front plate and the rear plate.

Other aspects and features of the disclosed systems and methods will be appreciated from reading the attached detailed description in conjunction with the included drawing figures. Moreover, selected aspects and features of one example embodiment may be combined with various selected aspects and features of other example embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

For further understanding of the disclosed concepts and embodiments, reference may be made to the following detailed description, read in connection with the drawings, wherein like elements are numbered alike, and in which:

FIG. 1 is a side view of an exemplary machine, according to one embodiment of the present disclosure;

FIG. 2 is a front view of an exemplary fan without a stiffener, the fan hub having a front plate and a rear plate that is obscured by the front plate;

FIG. 3 is a front view of the rear plate of FIG. 2.

FIG. 4 is a front view of the fan of FIG. 2 shown with the front plate removed;

FIG. 5 is a partial cross-sectional view of the fan of FIG. 2 taken along line 4-4;

FIG. 6 is a front view of a rear plate according to the disclosure, the rear plate defining apertures for accommodating fasteners for a stiffener;

FIG. 7 is a perspective view of a stiffener according to one embodiment of the present disclosure;

FIG. 8 is front view of the stiffener of FIG. 7;

FIG. 9 is a front view of a fan with one hub plate removed and including the stiffener of FIG. 7;

FIG. 10 is a front view a stiffener according to another embodiment of the present disclosure;

FIG. 11 is a front view of a fan with one hub plate removed and including the stiffener of FIG. 10;

FIG. 12 is a front view a stiffener according to another embodiment of the present disclosure;

FIG. 13 is a front view of a fan with one hub plate removed and including the stiffener of FIG. 12;

FIG. 14 is a front view a stiffener according to another embodiment of the present disclosure; and

FIG. 15 is a front view of a fan with one hub plate removed and including the stiffener of FIG. 14.

It is to be noted that the appended drawings illustrate only typical embodiments and are therefore not to be considered limiting with respect to the scope of the disclosure or claims. Rather, the concepts of the present disclosure may apply within other equally effective embodiments. Moreover, the drawings are not necessarily to scale, emphasis generally being placed upon illustrating the principles of certain embodiments.

DETAILED DESCRIPTION

An exemplary embodiment of a work machine 210 according to the present disclosure is shown in FIG. 1. The term “work machine” may refer to any machine that performs some type of operation associated with an industry such as mining, construction, farming or transportation. For example, the work machine may be a mining truck, an earth moving machine, an on-road truck, an off-road truck, a construction machine, a tractor, or a people hauler. The work machine 210 generally includes a machine frame 212 for supporting, among other systems and components, a cooling system 220 which will be discussed in greater detail below.

The work machine 210 may include a plurality of ground-engaging elements 214, in this case wheels. As should be appreciated by one of ordinary skill in the art, an engine may provide propulsion power for the ground-engaging elements 214 and may power a variety of other machine systems, including various mechanical, electrical, and hydraulic systems and/or components. The work machine 210 may also include an operator control station 216 including a variety of operator controls and displays useful for operating the work machine 210 and/or a dump body 218 which may be pivotal relative to the machine frame 212.

FIG. 2 is a front view of a fan 10. The fan 10 may be used as part of a cooling system for a machine such as the work machine 210 of FIG. 1. The fan 10 comprises a hub 12 and a plurality of blades 14 extending radially from the hub 12.

The hub 12 may comprise a first or front plate 16, a second or rear plate 18 (obscured in FIG. 2 by the front plate 16) and a central hub connection 20 (also obscured in FIG. 2). The front plate 16 and the rear plate 18 may have the same size and shape. Each plate 16, 18 may comprise an inner facing surface 22 that faces the central hub connection 20, an outer facing surface 24 and a perimeter 26 or outer diameter.

FIG. 3 is a front view of the rear plate 18 that is obscured in FIG. 2. Both the rear plate 18 and the front plate 16 may define a central bore 28, a plurality of blade fastener apertures 30 arranged around each plate 16, 18 near the perimeter 26, and a plurality of central hub connection fastener apertures 32 arranged circumferentially around and near the central bore 28.

FIG. 4 is a front view of the fan 10 of FIG. 2 shown with the front plate 16 removed, allowing a better view of the rear plate 18 in situ. The central hub connection 20 may be substantially annular in shape and may define an inner bore 34 having the same or a similar diameter to the central bore 28 of each plate 16, 18. The central hub connection 20 may have a cylindrical outer wall 36 which faces radially outward. The central hub connection 20 may define axially oriented central hub connection apertures 38 that align with the central hub connection fastener apertures 32 in the front plate 16 and the rear plate 18. The plates 16, 18 may be attached to the central hub connection 20 by any suitable means, such as rivets or bolts 40 that extend through the central hub connection fastener apertures 32 and the central hub connection apertures 38.

Each blade 14 may comprise a generally planar inner portion 42 configured to engage the hub 12, a generally curved distal portion 44 which may be angularly displaced from the plane of the hub 12, and an intermediate portion 46 which joins the inner portion 42 and the distal portion 44. The blade inner portion 42 may have an inner edge 52 and may define apertures 48 that align with the blade fastener apertures 30 in each plate 16, 18. Each blade 14 may be attached to the hub 12 and, more particularly, to the plates 16, 18 by any suitable means, such as rivets or bolts 40.

FIG. 4 is a perspective view of the fan of FIG. 2 with the hub front plate 16 removed for clarity. The blades 14 are positioned around the rear plate 18 with their distal portions 44 extending outwardly beyond the plate perimeter 26 and their inner portions 42 extending inwardly within the plate perimeter 26. The blade inner portion apertures 48 are aligned with the blade fastener apertures 30.

FIG. 5 is a cross-sectional view of the fan 10 of FIG. 2 taken along line 4-4. In this view it can readily be seen that there is a space or gap 50 between the front plate 16 and the rear plate 18 and between the outer wall 36 of the central hub connection 20 and the inner edges 52 of the blades 14. Between the blades 14, the gap 50 extends all the way to the plate perimeters 26 as perhaps better shown in FIG. 3. In other words, the front plate 16, the rear plate 18, the central hub connection 20 and the blade inner portions 42 define a gap 50 that may extend from the central hub connection 20 to the perimeters 26 of the plates 16, 18.

This gap 50 reduces fan hub stiffness, resulting in a low frequency fore-aft bending mode that causes high stresses in multiple locations on the plates 16, 18 close to the fan blades 14 and the central hub connection 20. The overall stiffness becomes even less as the hub diameter is increased.

FIG. 6 is a front view of a rear plate 18 modified to accommodate a stiffener. The front plate 16 may be similarly modified. The rear plate 18 may be substantially similar to the rear plate 18 described above with respect to FIG. 3, but further defines stiffener fastener apertures 33 for accommodating bolts 40 or other fasteners. The stiffener fastener apertures 33 may be located near the plate central bore 28 but radially distally of the central hub connection fastener apertures 32, and near the perimeter 26 between the groups or sets of blade fastener apertures 30. The stiffener fastener apertures 33 may be distributed evenly (symmetrically) around the central bore 28.

FIG. 7 is a perspective view of a stiffener 60 according to one embodiment of the present disclosure. FIG. 8 is front view of the stiffener 60 of FIG. 7. The stiffener 60 comprises a body 62 and a plurality of arms 64 extending radially outward from a perimeter 66 of the body 62. The body 62 may have a diameter and may have an annular inner wall 67 that defines a central bore 68. The annular inner wall 67 may have a diameter the same as or similar to the outer diameter of the central hub connection 20 so that the inner wall 67 of the stiffener 60 may abut (and fit snugly against) the central hub connection outer wall 36 as shown in FIG. 9. The stiffener 60 may have an outer diameter the same as or slightly smaller than the diameter of the plates 16, 18 so that the stiffener 60 does not extend beyond the perimeter 26 of the plates 16, 18. The stiffener 60 may be of uniform construction, that is, made of a single material, or can be made of multiple materials. In either case, the stiffener 60 may be symmetrical so that its weight (mass) is evenly distributed about the central bore 68.

The body 62 may define body apertures 70 for receiving fastening means such as bolts 40. Each arm 64 may define arm apertures 72 for receiving fastening means such as bolts 40. The body apertures 70 and arm apertures 72 may align axially with the stiffener fastener apertures 33 located in (defined by) each plate 16, 18.

The stiffener 60 may also define voids 74 throughout the body 62 and arms 64 to reduce weight while maintaining a satisfactory stiffness. The voids 74 may be any suitable size and shape, and may be oriented symmetrically about the stiffener central bore 68 to maintain an even distribution of the weight of the stiffener 60 about the bore 68.

FIG. 9 is a front view of a fan 10 with the front plate 16 removed and including the stiffener 60 of FIGS. 7 and 8. In other words, the view is the same as FIG. 4 but with the stiffener 60 (and a modified rear plate 18).

The stiffener 60 may extend radially from the central hub connection 20 to the perimeter 26 of the front plate 16 and the rear plate 18. The stiffener body perimeter 66 may be located anywhere between a location near the central hub connection 20 to a location at or near the inner edges 52 of the blades 14. Each arm 64 may extend outwardly from the body 62 between the inner portions 42 of adjacent blades 14 to a location near or at the perimeter 26 of the front plate 16 and the rear plate 18.

The stiffener 60 may completely or partially occupy the gap 50 between the front plate 16 (not shown in FIG. 9) and the rear plate 18. For example, the stiffener body 62 may substantially occupy the space between the front plate 16 and the rear plate 18 and between the central hub connection 20 and a location corresponding to the stiffener body perimeter 66, and the stiffener arms 64 may occupy some, most or all of the space between the blade inner portions 42.

The stiffener 60 may abut the central hub connection 20, the front plate 16 and the rear plate 18. The stiffener 60 may also abut the inner portions 42 of the blades 14 or, as shown in FIG. 9, the stiffener 60 may be slightly spaced apart from the inner portions 42 of the blades 14.

The stiffener 60 may be affixed to the front plate 16 and the rear plate 18 with fasteners such as bolts 40 or, more specifically, huck bolts. The stiffener 60 may be fastened to the front plate 16 and the rear plate 18 at different diametric (annular) locations about the central hub connection 20. For example, the stiffener 60 may be fastened to the front plate 16 and the rear plate 18 at the stiffener body 62 a short distance from the central hub connection 20 (where the stiffener body apertures 70 are located) and at the radially distal ends of the stiffener arms 64 near the perimeter 26 of the front plate 16 and the rear plate 18 (where the stiffener arm apertures 72 are located). The locations of the stiffener apertures 70, 72, and thus the fasteners 40, may be optimized to create a high level of hub stiffness and a low hub weight.

The stiffener 60 may be of unitary construction, that is, may be made of a single piece of material, or it may comprise multiple layers (thicknesses) of stiffener plates which can be stacked on top of one another so that the total axial thickness is substantially equal to the thickness of the gap 50 between the plates 16, 18. The stiffener 60 may be made of any suitable material, including steel.

FIG. 10 is a perspective view of a stiffener 80 according to another embodiment of the present disclosure. The stiffener 80 comprises a body 82 and a plurality of arms 84 extending radially outward from a perimeter 86 of the body 82. The body 82 may have a diameter and may have an annular inner wall 87 that defines a central bore 88. The annular inner wall 87 may have a diameter the same as or similar to the outer diameter of the central hub connection 20 so that the inner wall 87 of the stiffener 80 abuts (fits snugly against) the central hub connection outer wall 36 as shown in FIG. 11. The stiffener 80 may have an outer diameter the same as or slightly smaller than the diameter of the plates 16, 18 so that the stiffener 80 does not extend beyond the perimeters 26 of the plates 16, 18.

The stiffener body 82 may define apertures 90 for receiving fastening means such as bolts 40. In addition, each arm 84 may define apertures 92 for receiving fastening means such as bolts 40. The apertures 90, 92 may align with the stiffener fastener apertures 33 located in (defined by) each plate 16, 18. The stiffener body 82 may be solid with the exception of the apertures 90. Alternatively, the stiffener body 82 and/or the stiffener arms 84 may define voids 94 to reduce weight while maintaining a satisfactory stiffness. The voids 94 may be any suitable size and shape, and may be oriented symmetrically about the body central bore 88 to evenly distribute the weight of the stiffener 80 about the bore 88.

FIG. 11 is a front view of a fan with the front plate 16 removed and including the stiffener 80 of FIG. 10. As shown in FIG. 11, each stiffener arm 84 may extend between the inner portions 42 of adjacent blades 14.

FIG. 12 is a perspective view of a stiffener 100 according to another embodiment of the present disclosure. The stiffener 100 comprises a body 102 and a plurality of arms 104 extending radially outward from a perimeter 106 of the body 102. The body 102 may have a diameter and may have an annular inner wall 107 that defines a central bore 108. The annular inner wall 107 may have a diameter the same as or similar to the outer diameter of the central hub connection 20 so that the inner wall 107 of the stiffener 100 abuts (fits snugly against) the central hub connection outer wall 36 as shown in FIG. 13. The stiffener 100 may have an outer diameter the same as or slightly smaller than the diameter of the plates 16, 18 so that the stiffener 100 does not extend beyond the perimeters 26 of the plates 16, 18. The stiffener 100 may be of uniform construction, that is, made of a single material, or can be made of multiple materials. In either case, the stiffener 100 should be symmetrical so that its weight is evenly distributed about the central bore 108.

The body 102 may define apertures 110 for receiving fastening means such as bolts 40. Each arm 104 may define apertures 112 for receiving fastening means such as bolts 40. The apertures 112 may align with stiffener fastener apertures 33 located in (defined by) each plate 16, 18. The stiffener 100 may also define voids 114 throughout the body 102 to reduce weight while maintaining a satisfactory stiffness. The voids 114 may be any suitable shape, and may be oriented symmetrically about the body central bore 108 to maintain an even distribution of the weight of the stiffener 100 about the bore 108.

FIG. 13 is a front view of a fan 10 with the front plate 16 removed and including the stiffener 100 of FIG. 12. As shown in FIG. 13, each arm 104 may extend between the inner portions 42 of adjacent blades 14.

FIG. 14 is a perspective view of a stiffener 120 according to another embodiment of the present disclosure. The stiffener 120 comprises a body 122 and a plurality of arms 124 extending radially outward from a perimeter 126 of the body 122. The body 122 may have a diameter and may have an annular inner wall 127 that defines a central bore 128. The annular inner wall 127 may have a diameter the same as or similar to the outer diameter of the central hub connection 20 so that the inner wall 127 of the stiffener 120 abuts (fits snugly against) the central hub connection outer wall 36. The stiffener 120 may have an outer diameter the same as or slightly smaller than the diameter of the plates 16, 18 so that the stiffener 120 does not extend beyond the perimeters 26 of the plates 16, 18. The stiffener 120 may be of uniform construction, that is, made of a single material, or can be made of multiple materials. In either case, the stiffener 120 should be symmetrical so that its weight is evenly distributed about the central bore 128.

The body 122 may define apertures 130 for receiving fastening means such as bolts 40. Each arm 124 may define apertures 132 for receiving fastening means such as bolts 40. The apertures 132 may align with stiffener fastener apertures 33 located in (defined by) each plate 16, 18. The apertures 130, 132 may be arranged in one, two or more concentric circular arrays centered around the central bore 128.

FIG. 15 is a front view of a fan 10 with the front plate 16 removed and including the stiffener 120 of FIG. 14. As shown in FIG. 15, each arm 124 may extend between the inner portions 42 of adjacent blades 14.

INDUSTRIAL APPLICABILITY

In general, the teachings of the present disclosure may find broad applicability in many industries including, but not limited to, construction, agriculture, and road maintenance industries. More specifically, the present disclosure may find applicability in any industry using machines or equipment that include a fan based cooling system.

Referring to FIGS. 9, 11, 13 and 15, various stiffeners 60, 80, 100, 120 are disclosed that may be used in a fan based cooling system 220 of a kind used with work machines such as that shown in FIG. 1. The stiffener 60, 80, 100, 120 may be provided in dimensions appropriate for the size of the fan 10 and, in particular, the fan hub 12. In operation, the stiffener 60, 80, 100, 120 may add stiffness to the fan hub 12 while adding as little weight as possible. The stiffener 60, 80, 100, 120 may reduce fore-aft bending and the resulting stresses that can occur in previous fan hubs.

While the present disclosure has shown and described details of exemplary embodiments, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the disclosure as defined by claims supported by the written description and drawings. Further, where these exemplary embodiments (and other related derivations) are described with reference to a certain number of elements it will be understood that other exemplary embodiments may be practiced utilizing either less than or more than the certain number of elements. 

1. A fan hub comprising: a front plate comprising an inner facing surface and an outer facing surface, the front plate having a diameter and a perimeter; a rear plate comprising an inner facing surface and an outer facing surface, the rear plate having a diameter and a perimeter, the front plate and the rear plate each defining a central bore, a plurality of sets of blade fastener apertures arranged circumferentially around each plate near the plate perimeter, a plurality of central hub connection fastener apertures arranged circumferentially around the central bore, and a plurality of stiffener fastener apertures, the central bore, the blade fastener apertures, the central hub connection fastener apertures and the stiffener fastener apertures of the rear plate registering with the central bore, the blade fastener apertures, the central hub connection fastener apertures and the stiffener fastener apertures of the front plate; an annular central hub connection defining an inner bore registering with the central bores of the front plate and the rear plate, the central hub connection having a cylindrical outer wall facing radially outward, the central hub connection further defining central hub connection apertures registering with the central hub connection fastener apertures of the front plate and the rear plate; and a stiffener comprising a body and a plurality of arms extending radially outward from a perimeter of the body, the body defining a stiffener central bore registering with central bores of the front plate and the rear plate, the stiffener having an outer diameter no larger than the diameter of the front plate, each arm extending radially outward from the body and between adjacent sets of blade fastener apertures, the stiffener defining apertures for receiving fasteners, the stiffener apertures registering with some or all of the stiffener fastener apertures in the front plate and the rear plate.
 2. The fan hub of claim 1 wherein the stiffener has a mass that is evenly distributed about the central bore.
 3. The fan hub of claim 1 wherein the stiffener fastener apertures and the stiffener apertures are distributed symmetrically around the plate central bore.
 4. The fan hub of claim 1 wherein stiffener fastener apertures and the stiffener apertures are arranged in two or more concentric circular arrays centered around the central bore.
 5. The fan hub of claim 1 wherein 1 the stiffener defines voids oriented symmetrically about the stiffener central bore.
 6. The fan hub of claim 1 wherein the stiffener abuts the front plate and the rear plate and wherein the stiffener has an annular inner wall that abuts the central hub connection outer wall.
 7. The fan hub of claim 1 wherein the front plate, the rear plate and the central hub connection define a gap, and the stiffener is located in the gap.
 8. The fan hub of claim 1 wherein the stiffener is fastened to the front plate and to the rear plate at two or more annular locations about the central hub connection.
 9. The fan hub of claim 1 wherein the stiffener is fastened to the front plate and to the rear plate at the stiffener body a short distance from the central hub connection and at radially distal ends of the stiffener arms near the perimeter of the front plate and the rear plate.
 10. The fan hub of claim 1 wherein the stiffener is of unitary construction.
 11. The fan hub of claim 1 wherein the stiffener comprises multiple stiffener plates having a total axial thickness equal to an axial thickness of the gap between the plates.
 12. A fan comprising: a fan hub comprising a front plate, a rear plate and a central hub connection, the front plate comprising an inner facing surface and an outer facing surface, the front plate having a diameter and a perimeter, the rear plate comprising an inner facing surface and an outer facing surface, the rear plate having a diameter and a perimeter, the front plate and the rear plate each defining a central bore, a plurality of sets of blade fastener apertures arranged circumferentially around each plate near the plate perimeter, a plurality of central hub connection fastener apertures arranged circumferentially around the central bore, and a plurality of stiffener fastener apertures, the central bore, the blade fastener apertures, the central hub connection having a cylindrical outer wall facing radially outward and defining central hub connection apertures registering with the central hub connection fastener apertures of the front plate and the rear plate; a plurality of fan blades affixed to the fan hub, each blade comprising an inner portion located between the front plate and the rear plate; and a stiffener comprising a body and a plurality of arms extending radially outward from a perimeter of the body, the body defining a stiffener central bore registering with central bores of the front plate and the rear plate, the stiffener having an outer diameter no larger than the diameter of the front plate, each arm extending radially outward from the body and between adjacent sets of blade fastener apertures, the stiffener defining apertures for receiving fasteners, the stiffener apertures registering with some or all of the stiffener fastener apertures in the front plate and the rear plate.
 13. The fan of claim 12 wherein the stiffener has a mass that is evenly distributed about the stiffener central bore.
 14. The fan of claim 12 wherein the stiffener abuts the front plate and the rear plate and wherein the stiffener has an annular inner wall that abuts the central hub connection outer wall.
 15. The fan of claim 12 wherein the front plate, the rear plate, the central hub connection and the blade inner portions define a gap, and the stiffener is located in the gap.
 16. The fan of claim 12 wherein the stiffener comprises multiple stiffener plates having a total axial thickness equal to an axial thickness of the gap between the plates.
 17. A work machine comprising a cooling system with a fan, the fan comprising: a fan hub comprising a front plate, a rear plate and a central hub connection, the front plate comprising an inner facing surface and an outer facing surface, the front plate having a diameter and a perimeter, the rear plate comprising an inner facing surface and an outer facing surface, the rear plate having a diameter and a perimeter, the front plate and the rear plate each defining a central bore, a plurality of sets of blade fastener apertures arranged circumferentially around each plate near the plate perimeter, a plurality of central hub connection fastener apertures arranged circumferentially around the central bore, and a plurality of stiffener fastener apertures, the central bore, the blade fastener apertures, the central hub connection having a cylindrical outer wall facing radially outward and defining central hub connection apertures registering with the central hub connection fastener apertures of the front plate and the rear plate; a plurality of fan blades affixed to the fan hub, each blade comprising an inner portion located between the front plate and the rear plate; and a stiffener comprising a body and a plurality of arms extending radially outward from a perimeter of the body, the body defining a stiffener central bore registering with central bores of the front plate and the rear plate, the stiffener having an outer diameter no larger than the diameter of the front plate, each arm extending radially outward from the body and between adjacent sets of blade fastener apertures, the stiffener defining apertures for receiving fasteners, the stiffener apertures registering with some or all of the stiffener fastener apertures in the front plate and the rear plate.
 18. The work machine of claim 17 wherein the stiffener has a mass that is evenly distributed about the stiffener central bore.
 19. The work machine of claim 17 wherein the stiffener abuts the front plate and the rear plate and wherein the stiffener has an annular inner wall that abuts the central hub connection outer wall.
 20. The work machine of claim 17 wherein the work machine is one of a mining truck, an earth moving machine, an on-road truck, an off-road truck, a construction machine, a tractor, and a people hauler. 